We have recently heard of Samsung's plans for updating devices with their approximate time frame. The list is extensive and covers all cell phones for which Samsung plans an Android Pie Update. Of course, the Galaxy S9 and the Galaxy S9 + are on the list, and their Android Pie Update is scheduled for January. We've heard this information from other sources as well, but it looks like some Galaxy S9 and S9 + phones are already getting their pie updates.
The Android Pie-based One UI update has pounced in some cell phones across Europe and the Middle East. The build number is G960FXXU2CRLI and you can review the change log by clicking the following source link:
Apart from a BS bump on Pie, updating the One user interface is an important update that changes the user experience on the device. A user interface is also the next evolution of the Samsung user interface (formerly TouchWiz, then Samsung Experience) and is a major overhaul. As suggested in the support document, make sure you have a backup of your important information before you apply them as soon as you see them available on your phone.